Since a polyimide resin has characteristics such as excellent heat resistance, mechanical strength and insulation property, and low dielectric constant, a polyimide resin is used widely as an insulating material or protective material in electric or electronic parts including various elements or electronic substrates such as multilayered wiring board. Also, in order to selectively insulate or protect a minute point in precision electric or electronic parts, polyimide resin which has been provided with patterning to a desired shape is used.
Generally, a polyimide resin is an imide ring-containing polymer formed by subjecting polyamic acid obtained by polymerizing a tetracarboxylic dianhydride component and a diamine component in a polar organic solvent to heat treatment at a high temperature of approximately 300° C. Therefore, polyimide products for an electronic material are often supplied as a solution of a polyimide precursor, such as polyamic acid. In producing electric or electronic parts, a solution of a polyimide precursor is supplied to a site where an insulating material or protective material is to be formed by a method such as coating or injection, etc. and thereafter the solution of the polyimide precursor is subjected to heat treatment at a high temperature of approximately 300° C. to form the insulating material or protective material.
Conventional methods for forming an insulating material or protective material made of a polyimide resin from a polyimide precursor have problems in which such conventional methods are not applicable to material which is weak to heat, because the conventional methods require heat treatment at a high temperature. Accordingly, a polyimide precursor composition which is capable of forming a polyimide resin by the treatment at a low temperature, for example, approximately 200° C., has been developed (for example, Patent Document 1).
On the other hand, since polybenzoxazole resin has excellent heat resistance, mechanical strength, insulation property, dimensional stability, and the like, they are used as not only fiber or film, but also as an insulating material or a protective material in electric or electronic parts including various elements or electronic substrates such as multilayered wiring board.
Generally, polybenzoxazole resin is an oxazole ring-containing polymer formed by subjecting a precursor polymer obtained by polymerizing an aromatic diamine diol having an amino group and a hydroxyl group on the adjacent carbon atoms in the aromatic ring, a dialdehyde compound, and a dicarbonyl compounds such as dicarboxylic acid dihalide, in organic solvent such as N-methyl-2-pyrrolidone (NMP), dimethylacetamide (DMAc) and dimethylformamide (DMF) to heat treatment at a high temperature of approximately 300° C.
Specific examples of the thus produced oxazole ring-containing polymer include polybenzoxazole resin formed by subjecting a solution of a precursor obtained by reacting aromatic diamine diol having an amino group and a hydroxyl group on the adjacent carbon atoms in the aromatic ring with di(4-formylphenyl)alkane or di(4-halocarbonyl phenyl)alkane in dimethylformamide to heat treatment at a high temperature, in which the temperature is increased from 200° C. to finally 300° C. (for example, Patent Document 2).
Furthermore, use of a polymer including both an imide ring and an oxazole ring for a positive photosensitive resin composition has been proposed (for example, Patent Document 3).    Patent Document 1: Japanese Unexamined Patent Application, Publication No. 2009-19113    Patent Document 2: PCT International Publication No.
WO2012/137840    Patent Document 3: Japanese Unexamined Patent Application, Publication No. 2014-157297